From Vision to Reality: Research Investment Makes a Quantum Leap

The APL-developed all-optical switching device for the Laboratory's quantum computer is shown here as it is tested in a vacuum chamber. Credit: JHU/APL

The quest to create more powerful computers has focused on the development of a revolutionary machine that could solve problems beyond the reach of existing technologies.

Quantum computers, which operate using the peculiar properties of quantum mechanics, can perform calculations at speeds and volumes that conventional (or “classical,” in quantum parlance) devices could never physically match.

Because of the potential applications of this computing capability to so many APL-related research fields and projects, the Laboratory has invested in quantum research for more than two decades. Recently, two projects, in both the theoretical and experimental areas, have made significant progress.

APL’s Research and Exploratory Development Department (REDD) is home to the Quantum Information Group, which has been funded by Defense Advanced Research Projects Agency, Intelligence Advanced Research Projects Agency, and independent research and development awards since the mid-1990s. “The quantum team’s work is an example of how REDD initiates lines of research and exploratory development that anticipate the technology challenges APL sectors and business areas will face in the future,” says Department Head Jim Schatz.

Victor McCrary, now REDD’s emerging technology and innovation manager, and former business area executive for what is now the Research and Exploratory Development Business Area, describes APL’s long commitment to quantum computing research as “a good example of foresight and patient capital investment paying off.”

“APL has a long history in this area, and we have had success throughout the years,” says program manager Bryan Jacobs. “We have also been working to make quantum computers more accessible to more problems.” That has been one challenge facing quantum computing since its inception: Although quantum computers are immensely capable, it’s difficult to frame classical tasks in ways that can use them.

To understand the first project’s accomplishment, it’s necessary to understand some basics about quantum computers. These machines use a type of information called quantum bits, or qubits, which (just like normal silicon bits) can represent a 0 or a 1. What makes qubits special is that they can also represent both 0 and 1 at the same time. Their ability to do that makes them capable of doing vast amounts of calculations simultaneously. Devices known as logic gates are used to control the operation of qubits.

What the Laboratory’s quantum team has done involves the development of all-optical logic gates. These gates operate using something called the quantum Zeno effect, which relates to the way that physical observation of a quantum object affects its quantum state—in this case, its position. As Jacobs puts it, “A watched quantum pot really doesn’t boil.” If a quantum particle (like a photon) is observed frequently enough, its path through a logic gate can be controlled by another photon. The APL team has recently demonstrated all-optical (photon-based) switching of classical signals (made up of many photons), which is an important step toward developing a photonic quantum computer. “This technology, which we invented, could also be used in future telecommunications networks and ultra-low-power classical computers,” Jacobs says.

The second project relates to the Laboratory’s goal of making the quantum computer more useful for real-world problems. Several groups at APL analyze electromagnetic scattering data, a task that would benefit from the computational capacity of the quantum computer. “We worked with one team to formulate their problem in a way that the quantum computer can work on it,” says Jacobs. Initial results have proven useful to researchers.

APL’s quantum computing efforts began in the 1980s as a cryptography program. Passwords and cryptography keys work because even a very powerful classical computer would take many decades to duplicate (or “guess”) them; there are just too many possible combinations. This challenge is nothing for a quantum computer, which could process many combinations—potentially all of them—in hours, or less.

To counter that threat, quantum cryptography creates quantum passwords shared between users that are impossible to duplicate or crack, because the very act of observing them changes them. “Quantum cryptography is generally immune to what quantum computers can do,” says Jacobs.

Although quantum cryptography systems (with limited capabilities) exist today, quantum computing is the field with the greater and more complex technical challenges—and also the potential for world-changing breakthroughs, which the Quantum Information Group will be exploring for years to come.